Patent GB-502898-A (GB)
Title: Improvements in abrading or polishing machines
IPC: B24B21/18
Filed: 1937-07-22
Abstract: 502,898. Grinding amd polishing; automatic control systems. MATTISON MACHINE WORKS. July 22, 1937, No. 20322. Convention date, Jan. 15,. [Class 60] [Also in Groups XXXV and XL] A grinding or polishing machine for treating metal sheets &c. W comprises an endless abrasive belt B, which moves parallel to the movement of a reciprocating work-table, and also has lateral movement to distribute wear and avoid scratching the work. The machine comprises a bed 1 supported by end members and a pedestal 3, which has a column 4 carrying adjustably a head 5, beneath which a worktable is reciprocated on ways 2 on the bed. The table comprises a base 7 with brackets 8 at its corners, the brackets having secured thereto a flexible apron 10 upon which the work W rests, the apron resting slidably upon supporting bars 9, 9a, and also upon a resiliently and adjustably mounted roller 12 opposite the operative part of the abrasive belt B. The belt B runs over rollers 14 .. 17, of which the roller 14 is carried by a standard 20 and belt driven by an electric motor 23; the roller 15 is opposite the roller 12 and is carried by the head 5 and brackets 13a, 24, and the roller 16 is carried by rams 28, 28a adjustable by screws 30, 30a to tension the bolt. In order that the belt may be shifted continuously backwards and forwards laterally of its direction of travel, the roller 17 is mounted on a plate 33 pivoted at 34 to the head 5 and oscillated thereabout, the plate at its ends resting on machined faces 41 on the head and having end blocks 40 slotted at 46 to move over guide blocks 48 secured to the head 5 and having plates 49 engaging the upper faces of the blocks 40; dust excluding strips 43 are secured to the blocks and to the head 5, and bolts 51, 52 adjustable in the blocks 40, limit the oscillation of the plate by engagement with the block 48. The plate 33 is oscillated by its pivotal connection at 54, 55 with a pitman 56 having thereon a strap 57 engaging an eccentric 58 driven through speed reduction gearing from a reversible torque motor 60; the throw of the eccentric is greater than the range of movement defined by the bolts 51, 52, so that when the block 48 engages one of the screws, the motor 60 will stop until reversed. The belt continues to move laterally after the block has engaged one of the screws, until stopped and reversed by the means described below. The eccentric also may be turned, for hand operation of the plate 33 and roller 17, by a hand wheel 58a. The motor is controlled automatically to shift the belt through a predetermined range R, Fig. 6, by means of two photo-electric cells 65, 66 arranged so that when the edge E of the belt interrupts a beam of light from a source 67 to the cell 65 the motor runs forwardly, and when the edge E allows a beam of light from a source 68 to reach the cell 66, the motor is reversed. The cells and the light sources are carried by holders 76, 77, 82, 83 mounted adjustably on a frame 75 mounted on the head 5, and adjustable transversely of the belt by a screw 70. The motor, which is fed from directcurrent lines L<1>, L<2> has a series field-winding 82 and is controlled by reversing switches 83.. 86 operated by coils 87, 88, fed with alternating-current from mains L<1>, L<2>, and which also control two normally closed switches 92, 93 and two normally open switches 94, 95, the coils being controlled by two normally closed switches 96, 98 and normally open switches 97, 99; the switches 97, 99 are controlled by coils 100, 101. The excitation of the coils 100, 101 is under the control of two grid controlled gas discharge tubes 118, 119, which in turn are controlled by the cells 65, 66, the coils being situated in the anode circuits of the tubes, and the grid potentials of the tubes being controlled by the operation of the cells, the grid 124 of the tube 118 being normally at such a potential relatively tq the cathode 118 tHat the coil 100 is energized, and the potential being reduced when the cell 65 functions, whilst the normal potential of the grid 127 of tube 119 is below that required to operate the tube, and is raised, by operation of the cell 66 to excite the coil 101 ; these operations cause alternate forwards and backwards rotation of the motor 60 and hence the corresponding lateral movements of the belt B.